Throughout the nation and the world, industrial chemicals have been disposed by burying containers or by simply dumping chemical liquids onto the ground. Over time, buried containers degrade and leak, and the ground dumped liquids slowly seep permitting the chemical liquids to find their way into groundwater and surface water.
The few chemical barriers which have been constructed have been formed by the trench-and-fill technique, i.e., digging a trench in the flow path of a contaminant plume and then refilling the trench with a material that will either sequester (sorb or precipitate) or destroy the contaminant (Gillham, R. W., S. F. O'Hannesin, and W. W. Orth. 1993. Metal enhanced abiotic degradation of halogenated aliphatics: Laboratory tested and field trials, pp. 1-21. In: Papers Presented at the 1993 HazMat Central Conference. Mar. 9-11, 1993. Chicago, Ill.). The selection of the materials used for chemical barriers is dependent on the targeted contaminant, the remediation objective, and site conditions. In addition to these materials being good sequestering agents, they must also be inexpensive and possess a sufficiently high hydraulic conductivity to promote groundwater flow through the chemical barrier. Numerous materials have been proposed for "trench-and-fill" barriers including zeolite minerals, minerals modified with surface-bound chelates and quaternary amines, organic peat, limestone, titanium hydroxide, titanium oxide, fly ash, saw dust, lignite, hematite, magnetite, goethite, hydroxyapatite, andisols for anions, and zero-valent iron, Fe.sup.0. In the situation where an organic contaminant is destroyed by the chemical barrier (typically through chemical reduction or oxidation), the barrier itself can be left in place with minimal disturbance to the surface environment. In the situation where inorganic contaminants are sequestered by the barrier, the barrier may be left in the ground where it would be expected to release contaminants at a much slower rate than the natural sediment. If it is deemed necessary, the barrier and the concentrated contaminants could be excavated.
Trench-and-fill chemical barriers made of zero valent iron, Fe.sup.0, have been successfully field-demonstrated at a number of sites including a trichloroethylene plume in Sunnyvale, Calif., a trichloroethylene and tetrachloroethylene plume at the Borden Air Force Base, Canada (Gillham et al., 1993), a chlorinated hydrocarbon and chromate plume at the U.S. Coast Guard Support Center near Elizabeth City, N.C., and a chlorinated hydrocarbon plume at a former semiconductor manufacturing facility in the San Francisco Bay area. Although effective chemically, trench-and-fill remediation is costly and can only be used to remediate shallow plumes.
Another remediation of contaminated groundwater using extraction and surface treatment approaches (pump-and-treat) has repeatedly been shown to be an extremely costly proposition and the results have been generally ineffective.
Accordingly, there is a need for a cost effective method of intercepting the chemical liquids and preventing them from entering the groundwater and surface water.